Of Density, Curves And Contrast

  • Thread starter Thread starter Alan Smithee
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Alan Smithee

Can someone prime my brain about this....for the sake of simplicity I'm
talking black and white scanning photography here....
1) Film density plots out (logarithmically) on a curve usually an ESS or
upswept are common.
2) Silver bromide papers are said to "compliment" a film's curve, offsetting
the compressed ends of the exposure (dark and light) by curving also.
When a scanner scans a frame of film it's sensor is more or less "linear"
not curved like paper, true or false? Assuming true, therefore, shouldn't
the resulting scan ALWAYS require a contrast curve be applied to shape the
tones a bit to make it look more like a B&W photo? Shouldn't this correction
be relative to the shape of the original film's curve? Or am I just missing
something in this arguement. Thx.
 
Alan said:
Can someone prime my brain about this....for the sake of simplicity I'm
talking black and white scanning photography here....
1) Film density plots out (logarithmically) on a curve usually an ESS or
upswept are common.
2) Silver bromide papers are said to "compliment" a film's curve, offsetting
the compressed ends of the exposure (dark and light) by curving also.
When a scanner scans a frame of film it's sensor is more or less "linear"
not curved like paper, true or false? Assuming true, therefore, shouldn't
the resulting scan ALWAYS require a contrast curve be applied to shape the
tones a bit to make it look more like a B&W photo? Shouldn't this correction
be relative to the shape of the original film's curve? Or am I just missing
something in this arguement. Thx.
Click to expand...

Again, it depends upon the final paper for the print. There are curves that can
be applied to profile a file to more closely match a particular paper. However,
I am not convinced that is necessary on any inkjet papers.

Dan Burkholder has done some work in this direction. The intention has been
using commercial printing negatives, and a somewhat proprietary process, then
contact printing. When I learned it, the end use was either silver prints, or
platinum prints. Applying a curve to the digital file was one of the steps.

Ciao!

Gordon Moat
A G Studio
<http://www.allgstudio.com>
 
Alan said:
Can someone prime my brain about this....for the sake of simplicity I'm
talking black and white scanning photography here....
1) Film density plots out (logarithmically) on a curve usually an ESS or
upswept are common.
2) Silver bromide papers are said to "compliment" a film's curve, offsetting
the compressed ends of the exposure (dark and light) by curving also.
When a scanner scans a frame of film it's sensor is more or less "linear"
not curved like paper, true or false? Assuming true, therefore, shouldn't
the resulting scan ALWAYS require a contrast curve be applied to shape the
tones a bit to make it look more like a B&W photo? Shouldn't this correction
be relative to the shape of the original film's curve? Or am I just missing
something in this arguement. Thx.
Click to expand...

I have found that my scans are often improved if I apply an S-shaped
curvewith a toe and shoulder. But it is really highly dependent on the
particular image.
 
The sensor is linear. The scanner software/driver applies the
appropriate processing
(the non-linear curve or gamma as well as blackpoint/whitepoint) to
accomodate this. Unfortunately, the user has limited or no control over
this which is why you will find
that when scanning negatives (at least with most scanner vendor
software) you may
get loss of highlight or shadow detail.
 
The sensor is linear. The scanner software/driver applies the
appropriate processing
(the non-linear curve or gamma as well as blackpoint/whitepoint) to
accomodate this. Unfortunately, the user has limited or no control
over this which is why you will find
that when scanning negatives (at least with most scanner vendor
software) you may
get loss of highlight or shadow detail.
Click to expand...

Would it not make more sense to have a pre made curve for each film type
(upswept, Ess etc.) and then apply that to the RAW file? Also if I get a
file in which the entire histogram fits within the limits of scanners
capacity (say less than 8 stops to be safe) would I expect to lose either
highlight or shawdow detail? Probably not.
 
Regarding the film specific curves, some software (e.g. Silverfast)
attempts this. I think the issue
is 'lining up' the film curve with the scanner exposure and resulting
data. In a perfect word, everything is calibrated and
this would work well, in the real world I am not so sure.

Regarding highlight and shadow detail, correct, you should not lose
detail if the film dynamic range is
within the scanner dynamic range. However, with certain drivers (e.g.
Nikonscan) this definately happens,
especially with negative film. Again, I believe the software makes
internal decisions about what range of
data constitutes the image and throws out highs and lows beyond this. I
have seen this many times.
Silverfast also picks its own initial black and white points, but
allows the user to broaden the dynamic range if
he/she so chooses (Nikonscan does not). Vuescan also allows this, but I
have at times gotten inconsistent results
(I have not tried the newer versions)
 
Regarding the film specific curves, some software (e.g. Silverfast)
attempts this. I think the issue
is 'lining up' the film curve with the scanner exposure and resulting
data. In a perfect word, everything is calibrated and
this would work well, in the real world I am not so sure.

Regarding highlight and shadow detail, correct, you should not lose
detail if the film dynamic range is
within the scanner dynamic range. However, with certain drivers (e.g.
Nikonscan) this definately happens,
especially with negative film. Again, I believe the software makes
internal decisions about what range of
data constitutes the image and throws out highs and lows beyond this. I
have seen this many times.
Silverfast also picks its own initial black and white points, but
allows the user to broaden the dynamic range if
he/she so chooses (Nikonscan does not). Vuescan also allows this, but I
have at times gotten inconsistent results
(I have not tried the newer versions)
Click to expand...


The trick with NikonScan is to scan negatives
as positives. This adds about 30 seconds to
the overall scan-setup process.

It's described nicely in Dane Kosaka's site...

<http://www.marginalsoftware.com/LS8000Notes/three_easy_ways.htm>


rafe b.
http://www.terrapinphoto.com
 
Agreed, I do this also. But it is a relatively long laborious procedure
and there is no reason why the user should
have to go through this after paying alot of money for the scanner. Why
can't Nikon do it right?
While I'm at it, there is no reason why you should have to rescan to
try different settings of GEM etc.!!
Even the stock software that comes with much less expenisve Epson
flatbeds do not have this issue.

However, it is good of you to mention the alternate route of scanning
negs as positives as it does work.
 
While I'm at it, there is no reason why you should have to rescan to
try different settings of GEM etc.!!
Even the stock software that comes with much less expenisve Epson
flatbeds do not have this issue.
Click to expand...

Actually, there is a reason why you have to rescan. It's called
"licensing".

GEM, DEE and friends are all licensed by Nikon from Kodak. Obviously,
Nikon is not going to buy an unlimited license but will only want to
pay to use these 3rd party tools with their own scanners.

Not to defend Nikon, but this does make sense - probably the only
thing out of Nikon that does... ;o)

Anyone wishing to use these tools with other scanners can purchase
them from Kodak as Photoshop plug-ins. I think there are also
standalone versions. Kodak site should have all the info.

Don.
 
They (Nikon) should have figured out a clever scheme of locking their
files (e.g. embedding some
non-standard data or code) such that GEM etc. could be rexecuted on
files generated only by Nikonscan.
 
They (Nikon) should have figured out a clever scheme of locking their
files (e.g. embedding some
non-standard data or code) such that GEM etc. could be rexecuted on
files generated only by Nikonscan.
Click to expand...

That wouldn't work for many reasons. To name one, you then may not be
able to edit (or even view) such a file in any other program.

It would also be cracked (and rightly so) within minutes...

Proprietary file formats don't really work anymore. Just look at the
NEF nonsense.

BTW, have you checked the Kodak site? GEM (as well as ROC and SHO)
plug-ins are free to download for an unlimited trial period (saved
with a watermark). You could then implement the following workflow:

Scan once. Then use the GEM plug-in until you get the result you want.
The watermark wont bother you because you will not be saving the file
but only working with it live. After that you scan again with those
settings. That way you don't have to scan after each GEM change but
only scan twice in total. It's also easier working with the full image
in Photoshop, than with a tiny preview in Nikonscan.

Don.
 
Thanks for the suggestion, but in fact I have the GEM plugin. It seems
that the plugin is not quite the same beast as the version that is
embedded with the scanner code. Not a big deal in any case.
 
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